The present invention relates to a device for detachable coupling of an implement and the operating arm of an excavator together, said implement having an upper side with a forward edge facing the operating arm, said device comprising an attachment member which is supported by the stick and operating cylinder of the operating arm and comprises a shaft journalled horizontally at the stick, a shaft journalled horizontally at the operating cylinder, said shafts being parallel to and arranged at a predetermined distance from each other, and a hydraulic locking member comprising a hydraulic cylinder and a control unit for supplying the hydraulic cylinder with a predetermined operating pressure via a locking connection and an opening connection, which hydraulic cylinder has double pistons with piston rods facing away from each other which can be inserted and withdrawn to opening and locking position, the free outer end parts of said piston rods having a surface sloping outwardly to form locking wedges, each of the pistons defining a rear pressure chamber that forms the plus side of the piston, and a forward pressure chamber that forms the minus side of the piston, wherein the pressure area of the piston is greater on the plus side than on the minus side, said device also comprising an attachment member supported by the implement and comprising a coupling member and locking element, by means of which coupling member and locking element the implement attachment member is arranged to be detachably coupled to the attachment member of the operating arm under the influence of said hydraulic locking member, the implement thus being pivotable about the shaft of the stick by means of said operating cylinder, the attachment member of said operating arm comprising two link arms having a counter-support facing the implement and arranged below the shaft of the operating cylinder, which implement attachment member comprises two counter-supports arranged to cooperate with the counter-support of the link arms, which locking member is arranged to exert a pressure on the link arms in order to press these directly against the coupling member thereby achieving intimate contact between opposing support surfaces.
A device, known as a quick-coupling, with hydraulic locking members of the type described above is known through EP-0 139 652, see FIG. 8. The known device lacks satisfactory locking if a fault should occur in the hydraulic system and its locking wedges are unprotected and may therefore be damaged in inoperative positions. This may result in poorer locking function which in turn may deteriorate the influence of the link arms on the coupling member so that contact between the support surfaces of said counter-supports is insufficient and play occurs between them. Neither is the known locking member easy to install. SE-B-454 192 shows a similar quick-coupling but this lacks a hydraulic locking member.
EP-0 448 788 describes a quick-coupling with a hydraulic locking member but lacks the two attachment members which are significant for the quick-coupling described in EP-0 139 652 and according to the present invention with cooperating counter-supports, and also lacks a locking member with locking wedges to transfer compressive force at said counter-supports and eliminate play at their contact surfaces. No auto-adjustment of the locking positions of the locking pistons can therefore be obtained with the known locking member since wear appears gradually on the movable surfaces. It will be understood that the problem of play at opposing movable surfaces increases with increased wear.
The object of the present invention is to eliminate the problems discussed above and provide an improved device of the type described in the introduction, with a hydraulic locking member that ensures locking even if a fault should arise in the hydraulic system, where the locking wedges are protected from external influence in inoperating positions, which is easy to install, and which is self-adjusting upon wear in the contact surfaces so that play is eliminated and efficient locking and coupling functions are ensured even after extended use.
The coupling device according to the invention is characterized in that
by means of its end parts facing away from each other, the hydraulic cylinder is loosely mounted in corresponding, opposing openings in the link arms to form loose connections without locking engagement preventing axial movement of the hydraulic cylinder,
cooperating stop members are arranged on the hydraulic cylinder and at least one link arm to prevent rotation of the hydraulic cylinder in said openings,
the control unit is arranged to continuously supply the pressure chambers on the plus sides of the pistons with said predetermined operating pressure even when the locking wedges assume their withdrawn locking positions,
the control unit is arranged to supply the pressure chambers on the minus sides of the pistons with said predetermined operating pressure even when the locking wedges are moved from opening position to locking position and when the locking wedges assume their locking positions to achieve a controlled, reduced locking action of the locking wedges corresponding to the area difference on the plus and minus sides of the pistons, and
a pilot-controlled non-return valve is arranged in the locking connection between the control unit and the pressure chambers on the plus sides of the pistons, the non-return valve being openable to permit emptying of the pressure chambers on the plus sides of the pistons through the influence of said predetermined operating pressure, the non-return valve being connected via a branch connection to said opening connection for supplying said predetermined operating pressure when the locking connection is disconnected.